Ionic Bonds:
* Formation: Ionic bonds form when one atom (typically a metal) loses one or more electrons to become a positively charged ion (cation), while another atom (typically a nonmetal) gains those electrons to become a negatively charged ion (anion). The opposite charges then attract each other, forming the bond.
* Electron Transfer: Electrons are *transferred* from one atom to another.
* Electronegativity Difference: A large electronegativity difference between the atoms (typically greater than 1.7) is required for an ionic bond to form.
* Nature of Bond: The bond is primarily electrostatic attraction between the oppositely charged ions.
* Physical Properties: Ionic compounds tend to be:
* High melting and boiling points due to strong electrostatic forces.
* Hard and brittle because of the rigid lattice structure.
* Good conductors of electricity when dissolved or molten because the ions can move freely.
Covalent Bonds:
* Formation: Covalent bonds form when two atoms *share* one or more pairs of electrons.
* Electron Sharing: Electrons are shared between the atoms, creating a more stable electronic configuration for both.
* Electronegativity Difference: A smaller electronegativity difference (less than 1.7) is characteristic of covalent bonding.
* Nature of Bond: The bond arises from the mutual attraction of the shared electrons to the positively charged nuclei of the atoms.
* Physical Properties: Covalent compounds tend to be:
* Lower melting and boiling points compared to ionic compounds.
* Softer and more flexible.
* Poor conductors of electricity in solid and liquid states because the electrons are localized in the covalent bonds.
Summary Table:
| Feature | Ionic Bond | Covalent Bond |
|-------------------|-------------|----------------|
| Electron Transfer | Yes | No |
| Electron Sharing | No | Yes |
| Electronegativity Difference | Large | Small |
| Bond Strength | Strong | Variable |
| Physical Properties | High melting point, hard, brittle | Lower melting point, softer, flexible |
Example:
* Ionic Bond: Sodium chloride (NaCl) - Sodium loses an electron to become Na+ and chlorine gains an electron to become Cl-. The opposite charges attract, forming an ionic bond.
* Covalent Bond: Water (H₂O) - Hydrogen and oxygen share electrons to form covalent bonds.
Note: The distinction between ionic and covalent bonds is not always absolute. There are cases where a bond might be partially ionic and partially covalent, known as polar covalent bonds. This happens when the electronegativity difference is not large enough to completely transfer an electron, but significant enough to create a partial charge separation within the molecule.
